A variable gain amplifier has phase characteristics varying according to gain variation. A technique of maintaining phase characteristics constant is disclosed in Japanese Patent No. 3214463. In this reference, phase characteristics of a variable gain amplifier are compensated by a correction circuit added to the variable gain amplifier. The correction circuit has inverted phase characteristics to the phase characteristics of the variable gain amplifier. The variable gain amplifier is capable of maintaining the phase characteristics constant irrespective of gain variation by varying the phase characteristics of the correction circuit corresponding to the gain of the variable gain amplifier.
However, with the technique disclosed in Japanese Patent No. 3214463, the variable gain amplifier is required to include the correction circuit. Accordingly, circuit size of the variable gain amplifier becomes larger.